The present invention relates to fluids useful as subterranean treatment fluids, and, at least in some embodiments, to novel silica control agents used with fracturing fluids, and their associated methods of use.
A wellbore in a subterranean formation may penetrate portions of the formation that may be susceptible to degradation. Formation degradation, such as swelling, sloughing, and/or release of fines, may substantially decrease the stability of the wellbore. In an extreme case, degradation may decrease the stability of the wellbore to such an extent that the wellbore collapses.
Many formation strata, particularly sandstone, shale, and/or clay, are reactive with water, resulting in ion exchange and absorption of aqueous fluids. The presence of aqueous fluids, such as formation fluids or treatment fluids, may lead to significant swelling of the strata and corresponding reductions in the mechanical strength of the subterranean formation. Moreover, the fine aggregate that composes the strata can pose problems if exposed to high stresses (e.g., shear and pressure from the flow of hydraulic fracturing fluids). For example, under high stress, shale can mechanically fail, resulting in the generation of fine clay materials that can be highly mobile in produced fluids. This can result in wellbore sloughing and large quantities of solids production, plugging screens and/or filling separators on the surface. To combat these problems, heretofore, brines that contain high ion concentration have been used in an attempt to reduce ion exchange and the reactivity of the strata.
Hydraulic fracturing may be useful for increasing the conductivity of a subterranean formation. Hydraulic fracturing operations generally involve pumping a treatment fluid (e.g., a fracturing fluid) into a wellbore that penetrates a subterranean formation at a sufficient pressure to create or enhance one or more pathways, or “fractures,” in the subterranean formation. An example of a hydraulic fracturing operation useful for shale formations is “high rate water frac,” wherein large volumes of an aqueous treatment fluid are injected into a wellbore at a high fluid flow rate. Treatment fluids often comprise aqueous solutions in which the ionic content has been adjusted to reduce clay swelling and/or clay and fines dispersion, but which may result in reduced fracture porosity. The treatment fluid may comprise particulates (e.g., proppant particulates) that are deposited in the resultant fractures. The particulates may help prevent the fractures from fully closing upon release of the hydraulic pressure, forming conductive channels through which fluid may flow between the formation and the wellbore. However, pumping particulate slurries through a tubular conduit, such as a steel pipe, may scrape, scour, and/or erode the interior surfaces of the tubular conduit. The damage to the interior surfaces may increase with the pumping rate. Consequently, high rate water frac operations may be more susceptible to such damage.
Exposed formation surfaces and the surfaces of particulates used in treatment fluids generally comprise minerals, which may react with other substances (e.g., water, minerals, treatment fluids, and the like) disposed in the subterranean formation. Such chemical reactions may be caused, at least in part, by conditions created by mechanical stresses on those minerals (e.g., fracturing of the mineral surfaces or the compaction of particulates). One type of stress-activated reaction may be diageneous reactions. As used herein, the terms “diageneous reactions,” “diageneous reactivity,” and “diagenesis” include any chemical and/or physical process that, in the presence of water, moves a portion of the mineral in a particulate and/or converts a portion of the mineral in a particulate into some other form or material. A mineral that has been so moved or converted is herein referred to as a “diageneous product” or “diagenic product.” Any formation surface or particulate comprising a mineral may be susceptible to diageneous reactions, including silicate minerals (e.g., quartz), silicates and glass materials, metal oxide minerals, and the like. Diagenesis reactions are thought to occur where two water-wetted mineral surfaces are in contact with each other at a point under strain. The localized mineral solubility near that point under strain may increase, causing the minerals to dissolve. Minerals in solution may then diffuse through the water film outside of the region where the mineral surfaces are in contact, where they may precipitate out of solution. The precipitate can plug the formation or screens, resulting in a decrease in production.